The U.S. has shut its southern border to livestock imports again after a flesh-eating parasite was found further north in Mexico than previously reported, raising alarm among American agriculture officials.

The flesh-eating livestock pest New World screwworm has advanced closer to the U.S. border with Mexico, the U.S. Department of Agriculture said, prompting Washington to block imports of Mexican cattle just days after it allowed them to resume at a port of entry in Arizona.